Chesapeake Bay Crater Offers Clues to Ancient Cataclysm

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Earlier estimates had suggested the crater was about a mile deep (1.3 kilometers) and 53 miles (85 kilometers) wide.

The impact of the bolide disturbed the normal layering of sediment, rocks, and aquifers, and water from many of the wells in the region is salty or brackish.

Utility companies in eastern Virginia are funding some of Powars' work because the findings have a direct bearing on the search for fresh groundwater needed to supply growing populations in the region.

Linked With Extinction?

Scientists have long suspected that the heat from the impact incinerated every living thing within hundreds of miles. The core drilling has revealed a zone of silt that is devoid of signs of indigenous life, lending credence to that hypothesis, said Poag.

Poag believes the impact could have influenced an extinction that occurred about 33 million years ago.

The early Oligocene extinction dramatically affected land mammals. Forest dwellers declined as forested habitat became less abundant, while hoofed animals flourished as a result of increasing temperate grasslands. A number of predators also became extinct at this time, mainly because of changes in vegetation.

The asteroid or comet that struck the area that later became the Chesapeake Bay may be evidence of a 2 million-year-long comet shower that scientists think may have occurred between 36 and 34 million years ago.

An even bigger crater in Popigai, northern Siberia, was created at about the same time. Scientists also have found traces of helium 3, an isotope associated with extraterrestrial objects, in sediment layers in Massignano, Italy, and other places dating to 35 million years ago.

"Global paleo-temperatures during the early Eocene show the world was getting cooler," said Poag. "Around 35 million years ago, at the end of the Eocene, there was a warm pulse, and for a short period of time the Earth warmed. Then beginning at around 34 million years ago the Earth cooled very rapidly. At 33.4 million years ago there was a major extinction event."

The aftermath of the bolide collision, Poag said, would have been prolonged darkness and acid rain caused by the fallout of rocks, dust, and particles that were blasted into the atmosphere, along with the residual effects of raging wildfires.

These conditions, he suggests, would cause the abrupt cooling of Earth, leading to the extinction that eventually occurred.

The National Geographic Society provided funding for this research in the past.

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